Alkaline electrochemical cells are typically configured as elongated cylindrical cells (e.g., AA-, AAA-, C- and D-size cells) or as flat cells (e.g., prismatic cells and button cells). Primary alkaline cells include a negative electrode (anode), a positive electrode (cathode), an electrolyte, a separator, a positive current collector and a negative current collector. The cathode of a conventional primary alkaline electrochemical cell comprises manganese dioxide (MnO2) and a conducting carbonaceous material, typically graphite, such as synthetic, natural, or expanded graphite or mixtures thereof as widely recognized in the art in a mixture wetted with an aqueous alkaline electrolyte such as potassium hydroxide. In cylindrical cells, the cathode mixture is compressed into annular rings and stacked in the battery can or the mixture may be extruded directly into the can, which serves as the positive current collector.
The anode of a primary alkaline cell generally comprises zinc or zinc alloy particles of various dimensions and shapes disposed in an alkaline electrolyte, such as potassium hydroxide, along with gelling agents such as carboxymethylcellulose (CMC) and other additives such as surfactants. A negative current collector, usually a brass pin or nail, is placed in electrical contact with the gelled anode. A separator placed between the electrodes enables ions, but not electrons, to transfer between the cathode and anode while preventing the materials from directly contacting each other and creating an electrical short circuit. Conventionally, the separator is a porous, non-woven, fibrous material wetted with electrolyte. The separator is typically disposed radially inwardly of the cathode. Other aspects of a conventional alkaline cell are well known.
With the successful commercialization of these primary cells in the marketplace, new approaches to designing cells with long service life, acceptable shelf life, and voltage characteristics that operate common portable devices continue to be developed.
However, the low density of the manganese dioxide material and its consumption of water during the discharge reaction of conventional zinc manganese dioxide alkaline electrochemical cells (requiring the designer to provide the necessary water) limits the amount of space available for the zinc anode (which determines the service life), thereby leading to relatively low volumetric energy density. A recognized alternative cathode material is copper oxide, which has a high material density, does not consume water in the electron discharge reaction, has a flat discharge curve, high volumetric energy density, and little volume expansion upon discharge. Although it appears to be an excellent candidate for a long service life battery, the operating voltage of conventional batteries having a zinc anode and a copper oxide cathode is unfortunately no more than approximately 1.05V, too low to operate modern day electronic devices at reasonable current drains. At any substantial device current drain, it can fall significantly below 1V, rendering the device largely inoperable.
The use of sulfur compounds to enhance the operating voltage of a battery having a CuO cathode is known. However, it is recognized in the art that soluble sulfur species produced in the presence of alkaline electrolyte are detrimental to both anode performance and shelf life. The commercial application is therefore limited.
Additionally, recent approaches disclose using expanded graphite and/or graphitic nano-fibers with CuO to produce a cell having long service life. However the operating voltage in such systems is typically around 0.7V. Notably many of the prior approaches fail to mention soluble copper species that can be detrimental to the anode, provide no means for mitigating the problem, and fail to recognize the significance of surface area of CuO particles or of active sites on the particles on the cell discharge voltage and performance. Therefore, the disclosed technology does not produce a viable battery with reasonable shelf life.